This invention relates generally to an improved diaphragm valve and, more particularly, to a diaphragm flow valve having no dead volume and no internal interconnecting fluid passages.
In many applications, it is desirable to regulate the flow of fluids in a manner minimizing intermixing of the fluids and cross-contamination therebetween. Such is the case, for example, in the apparatuses described in U.S. Pat. No. 4,008,736 to Wittmann-Liebold, et al., U.S. Pat. No. 4,252,769 to Hood, et al., and co-pending U.S. patent application Ser. No. 190,100 of Hood, et al now abandoned. Each of the above-listed apparatuses is designed for the sequential performance of a large number of chemical processes on a relatively small sample of chemical material. The results achieved in each successive chemical step in the sequence is thus entirely dependent on the purity of the sample and the other chemical components of the system following the preceding steps. The large number of chemical steps performed with such apparatuses also requires that the performance characteristics of all system components be sustainable over relatively long periods of use.
The valve arrangement of Wittmann-Liebold U.S. Pat. No. 4,008,736 includes a valve block having an elongated zig-zag passage therethrough, the zig-zag passage having a plurality of openings communicating with respective valving sites thereon. Fluid communication with the elongated passage is regulated by a plurality of apertured sliding blocks engaging the valve block at the valving sites thereof. The apertured blocks are actuable alternatively between conditions of communication and non-communication between the aperture therein and the corresponding opening in the valve block. The zig-zag configuration of the Wittmann-Liebold zig-zag passage has the advantage of permitting the valve arrangement to be easily flushed of residual fluids, however, the individual sliding blocks tend to wear considerably, causing leaks both to the atmosphere and between the various passages and apertures. Leaks of this nature produce contamination of the system from the atmosphere and cross-contamination between successive steps or cycles of the system itself. Contamination of this nature has a cumulative effect on the chemistry within the apparatus over a large number of cycles of operation.
The apparatus of the above-listed Hood, et al. application Ser. No. 190,100, now abandoned, includes a valve block having a zig-zag primary passage of the Wittmann-Liebold type, and a plurality of secondary conduits terminating in additional openings at the respective valving sites. Diaphragms extending across the valving sites are alternatively drawn away from and forced against the surface of the block by vacuum and positive gas pressure, respectively, to open and close a fluid pass between the openings at the valving site. While this configuration significantly improves upon the performance achievable with the Wittmann-Liebold valve, its performance is less than optimum in several respects. For instances, while the positive air pressure used to force the diaphragms against the valving sites is sufficient to terminate the flow of fluids between the openings at each valving site, it is sometimes incapable of completely expelling the last traces of fluid from the area between the valving site and the diaphragm. This problem becomes most acute after much use of the valve arrangement when the diaphragm becomes slightly stretched or puckered. Small pockets of residual fluid can then be trapped beneath a diaphragm away from the corresponding opening when the particular valve is closed. These residual traces of fluid are not susceptible to being flushed by a flow through the primary passage. Also, these valves can lead to system contamination in the event of a power failure or a minute perforation of a diaphragm. A power failure can eliminate the source of pressure necessary to close the valves while a ruptured diaphragm can result in the direct application of either vacuum or pressurized gas to the openings at the valve sites.
The above noted problems resulting from stretched or ruptured diaphragms are rendered more serious by the fact that the fluid, et al. valves are opened by applying a vacuum to the surface of the diaphragm to draw them upwardly into recesses of predetermined volume. The diaphragms are thus made to substantially conform to the shape of the recesses each time the individual valves are opened. The diaphragms are thus constantly being stretched and stressed during operation, increasing the likelihood that they will eventually rupture or fail to return to their original configuration.
The fluid, et al. valve apparatus is also rather expensive to install and to maintain, due primarily to the need for vacuum and high-pressure sources, lines and associated valves.
Therefore, in many applications, it is desirable to provide a valve apparatus which is modular in design and minimizes the various possibilities of fluid contamination over a large number of operating cycles.
More recently, there has been invented a valve apparatus of Stark, copending U.S. patent application Ser. No. 300,184. The Stark valve apparatus comprises a valve block means having at least one substantially flat varying site on a surface thereof, said valve block means defining primary and secondary passages communicating with said valving site through primary and secondary openings, respectively. The valve block is an elongated block of rectangular cross-section having a continuous primary passage in a sawtooth or zig-zag pattern formed by cross-drilling the valve block from the upper surface thereof. The primary passage is thus a continuous passage communicating at alternating intersections thereof with a plurality of valving sites on the surface through corresponding openings. A resilient diaphragm means covers the valving site and forms a fluid tight seal with the valve block means along the periphery of the valving site. At least one closure element is provided having a substantially flat closure surface, the closure element being actuable between an open condition wherein the closure surface is retracted a preselected distance from the valving site and the diaphragm means, and a closed condition wherein the closure surface forces the diaphragm means against the valving site. In this way, the diaphragm means can be urged away from the valving site by fluid pressure in the passage when the closure element is in the open condition, establishing a valve chamber above the valving site for fluid flow between the passages, and is forced against the valving site when the closure element is in the closed condition, eliminating said valve chamber and expelling any fluid therein.
The passages in the Stark valve have a series of internal intersections which are difficult to machine accurately, resulting in high production costs. The present invention avoids this serious problem by eliminating the internal intersections within the valve block and represents an important advance in this art.